Short-term effects of black tea on vascular function in healthy adults

INTERVENTION: 15 healthy men and women 18 to 75 years old will be recruited from the general population. Volunteers will have no history of major chronic disease. A randomised, controlled, cross‐over designed trial will be performed. Each participant will complete 3 visits in random order. Prior to each visit participants will be asked to consume a standard meal for dinner (the night before their visit) and a low‐fat breakfast (on the morning of their visit). Prior to the first visit, participants will be asked to document the meals so that they are able to repeat them for subsequent visits. For each visit participants will attend the School of Medicine and Pharmacology Research Unit at Royal Perth Hospital in the morning 2.5 hours after breakfast. Participants will consume for 28 days, 3 cups per day (morning, during the day and afternoon/evening), of the following beverages: 1. Hot water (200 ml) 2. Black tea (2 g tea leaves infused in 200 ml) 3. Black tea with added milk (2 g tea leaves infused in 200 ml plus 20 ml of low fat [1.5%] milk) The order of beverage consumption will be randomly assigned. There will be no washout between periods. On the morning of each visit, participants consume 1 cup of their assigned beverage with their breakfast meal, then a second cup 1.5 hours later. One hour after this they will attend the clinic for assessments of outcomes. All teas will be matched for total polyphenol content. Adherence will be monitored using participant diaries, tea bag counts and measurement of biomarkers of tea‐derived flavonoid exposure in urine. CONDITION: endothelial function high blood pressure PRIMARY OUTCOME: Primary outcome: endothelial function (flow‐mediated dilation) ; Flow‐mediated dilation (FMD) of the brachial artery will be measured non‐invasively using ultrasound. This measurement will be performed 1.5‐2.0 hours after the last beverage, and again 3.0‐3.5 hours after the last beverage. ; A trained ultrasonographer dedicated to the research protocol and blinded to the interventions used will perform all measurements according to a published protocol. Briefly, subjects are studied in a quiet, temperature‐controlled room (21 to 25 degrees Celcius) while resting in a supine position. Participants rest for 15 minutes in the supine position before initiation of FMD measurement. The left arm is extended and supported comfortably on a foam mat. ECG is monitored continuously. For the ultrasound, a 12‐MHz transducer connected to an Acuson Aspen 128 ultrasound device (Acuson Corp.) is fixed in position with a clamp over the brachial artery 5 to 10 cm proximal to the antecubital crease. After a baseline artery diameter recording of 1 min, a blood pressure cuff is placed around the left forearm and inflated to 200 mm Hg. The cuff is released after 5 min, inducing reactive hyperemia. The brachial artery image is then recorded for 4 min (240 seconds) after cuff deflation to assess flow‐mediated dilatation. Images are downloaded for retrospective analysis. Analysis of FMD of the brachial artery is performed with semi‐automated edge detection software, which automatically calculates the brachial artery diameter, corresponding to the internal diameter. This is gated to the R wave of ECG, with measurements taken at end diastole. Responses are calculated as the percentage change in brachial artery diameter from baseline. The FMD is measured at 10 second intervals to 240 seconds after cuff deflation. ; The primary outcome measure is the mean FMD between 60 seconds and 240 seconds. Analysis will also be performed using peak FMD as a secondary outcome. ; SECONDARY OUTCOME: Secondary outcome: arterial stiffness ; Faecal samples will be used to measure faecal microflora and will be frozen until later analysis. Secondary outcome: home blood pressure ; Arterial stiffness will be assessed non‐invasively using the SphygomCor pulse wave analysis system. Measurements of pulse wave velocity, central blood pressure and augmentation index will be performed at 2.0‐2.5 hours after the last beverage (5 replicates). The carotid–femoral pulse wave velocity is measured after 5 min rest in a supine position by applanation tonometry using the Sphygmo‐ Cor pulse wave analysis system (AtCor Medical, Sydney, Australia. Model MM3. Software version 9). Before measuring pulse wave velocity, systolic and diastolic blood pressure, measured using the Dinamap PRO 100 oscillometric recorder, are entered. The ECG is recorded throughout the procedure. Pulse waves are recorded at the carotid and then femoral locations. The pulse wave velocity is calculated from measurements of pulse transit time and distance travelled by the pulse wave. The augmentation index is measured from the peripheral pulse pressure curve registered at the radial artery. Secondary outcome: faecal microflora ; Participants will monitor their home blood pressure in the morning, afternoon and evening each day for the last 7 days of each of the 3 intervention periods. During each 7‐day home blood pressure measurement period, participants measure their blood pressure: (i) in the morning 30 minutes after waking and prior to breakfast; (ii) in the afternoon between lunch and dinner; and (iii) in the evening 1‐2 hour after dinner. Blood pressures will be measured using an A&D Medical UA‐67PC digital blood pressure monitor (A&D Instruments Ltd.). After a 5‐min rest in a seated position, 5 blood pressure measurements are performed with a 1‐min interval between measurements. The first reading is discarded. Secondary outcome: home heart rate ; Participants will monitor their home heart rate in the morning, afternoon and evening each day for the last 7 days of each of the 3 intervention periods. During each 7‐day home hear rate measurement period, participants measure their heart rate: (i) in the morning 30 minutes after waking and prior to breakfast; (ii) in the afternoon between lunch and dinner; and (iii) in the evening 1‐2 hour after dinner. Heart rate will be measured using an A&D Medical UA‐67PC digital blood pressure monitor (A&D Instruments Ltd.). After a 5‐min rest in a seated position, 5 heart rate measurements are performed with a 1‐min interval between measurements. The first reading is discarded. Secondary outcome: office blood pressure Secondary outcome: office heart rate INCLUSION CRITERIA: men and women Aged 18 to 75 years old No history of major chronic disease.